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Does anyone know (or know where I can find) a more detailed history of the development of our favorite pist- (well, favorite non-1911) ol? I mean like the names of the designer(s), how they went about it, interesting anecdotes, etc. I know it hasn't been around 100 years to have nearly the rich history of John Brownings gun, but I'm curious to know what happened between the day someone imagined it and now. Searched and didn't really find anything good on here.

Jim
 

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How the XD Works
by Dick Metcalf
The XD design integrates classic autoloader mechanics with several distinctly unconventional features. The basic operating mechanism employs a familiar Browning-type cam-ramp, tilt-barrel operation with a captive dual-spring recoil guide assembly. The noncockable ignition mechanism is striker-fired and requires a partial rearward motion of the slide (approximately 3/4 inch) to cock the system and ready the trigger. If the gun is dry-fired, or in the event of a misfire, the trigger cannot accomplish a repeat strike until/unless the slide is racked. In external aspect, this system appears to operate (and feel) much like the familiar mechanism of a Glock, as does the hinged "Glock-like" trigger-safety lever that prevents rearward trigger movement unless depressed by the user's trigger finger. However, the actual operating mechanics of the two designs are greatly different.

The XD mechanism completely cocks (preloads) the spring-charged firing pin so that the only function provided by the trigger pull is to release the sear and fire the gun. By contrast, the Glock "Safe Action" only partly preloads the firing mechanism, and the trigger pull physically completes the cocking action as well as releasing the firing pin. The XD is therefore a true "single-action" trigger design because its trigger only performs one function--releasing the firing mechanism. The Glock is a true "double-action" trigger design in that its trigger contributes to the actual cocking of the mechanism as well as releasing it.

To describe the process in detail: After the XD slide travels rearward about 3/4 inch, the spring-loaded sear "captures" a cocking lug on the firing pin, holding the pin compressed fully to the rear against the pressure of the firing pin spring when the slide travels back forward (either after a short manual retraction of the slide or after the slide's full rearward travel in the firing cycle). A pull on the trigger then moves the trigger bar and firing pin safety lever linkages forward, depressing the sear and releasing the firing pin to fire the cartridge. The XD pistol may "feel" like a DAO (double action only) mechanism, but it is not. It acts like a DAO, but it isn't, mechanically. Springfield's official term for the mechanism is Ultra Safety Assurance Action Trigger System--or "USA Action" for short.

Another unique XD design aspect is the grip safety that prevents the gun's trigger from being squeezed unless it is fully depressed. The XD grip safety also freezes the slide. If the grip safety isn't down, you can't pull the trigger, and you can't pull the slide to the rear to load an empty chamber or clear a loaded chamber. You also can't lock the slide back on an empty gun, whether the magazine is in or out. Plus, there is a separate internal firing pin block that is deactivated only when the trigger is pressed all the way rearward to the point of striker release.
 
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